ENGINEERING PHYSICS PHY101/102

1. Two waves of the same frequency have amplitudes 1.00 and 2.00. They interfere at a

point where their phase difference is 60.00 . What is the resultant amplitude?

2. Light of wavelength 624 nm is incident perpendicularly on a soap film(refractive

index =1.33) suspended in air. What are the least two thicknesses of the film for

which the reflections from the film undergo fully constructive interference ?

3. Suppose Young’s experiment is performed with blue green light of wavelength 500

nm. The slits are 1.20 mm apart, and the viewing screen is 5.40 m from the slit. How

far apart are the bright fringes?

4. In a double slit experiment the distance between slits is 5.0 mm and the slits

are 1.0 m from the screen. Two interference patterns

can be seen on the screen: one due to light with

wavelength 480 nm, and the other due to light with

wavelength 600 nm. What is the separation on the

screen between the third order (n = 3) bright fringes of

the two interference pattern?

5. A single slit is illuminated by light of wavelength and , chosen so the first

diffraction minimum of the component coincides with the second minimum of

the component. (a) What relationship exists between the two wavelengths? (b) Do

any other minima in the two diffraction pattern coincide?

6. A source containing a mixture of hydrogen and deuterium atoms emits red light at

two wavelengths whose mean is 656.3 nm and whose separation is 0.180 nm. Find

the minimum number of lines needed in a diffraction grating that can resolve these

lines in the first order.

7. Assume that the limits of the visible spectrum are arbitrarily chosen as 430 nm and

680 nm. Calculate the number of rulings per millimeter of a grating that will spread

the first order spectrum through an angle of 200 ?

8. Explain Young’s double slit experiment and obtain an expression for the fringe width

on the screen in terms of distance to the screen, the wavelength of light used and the

slit separation.

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ENGINEERING PHYSICS PHY101/102

9. Suppose two identical waves are traveling in opposite directions and are represented

by

Obtain an expression for the interference of these two sinusoidal waves.10. Find the sum y of the following quantities:

11. A broad beam of monochromatic light is directed perpendicular through two glass

plates that are held together at one end to create a wedge of air between them. An

observer intercepting light reflected from the wedge of air , which acts as thin film,

sees 4001 dark fringes along the length of the wedge. When the air between the plate

is evacuated, only 4000 dark fringes are seen. Calculate the index of refraction of air

from these data. Take the refractive index of vacuum as unity.

12. Bright light of wavelength 585 nm is incident perpendicularly on a soap film

of thickness , suspended in air. Is the light reflected by the two

surfaces of the film closer to interfering fully destructively or fully constructively?

13. Sound waves with frequency 3000 Hz and

speed 343 m/s diffract through the

rectangular opening of a speaker cabinet and

into a large auditorium. The opening which

has horizontal width of 30 cm faces a wall

100 m away. Where along that wall will a

listener be at the first diffraction minimum and thus have difficulty hearing the

sound?(neglect reflections)

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ENGINEERING PHYSICS PHY101/102

14. At night many people see rings (called entopic halos) surrounding bright outdoor

lamps in otherwise dark surroundings. The rings are the first of the side maxima in

diffraction patterns produced by structures that are thought to be within the cornea (or

possibly the lens) of the observer’s eye (the central maxima of such patterns overlap

the lamp).

a. Would a particular ring become smaller or larger if the lamp were

switched from blue to red light?

b. If a lamp emits white light, is blue or red on the outside edge of the ring?

Give reasons for your conclusions for questions (a) and (b)

15. White light with a uniform intensity across the visible wavelength range of 400 to 690

nm, is perpendicularly incident on a water film, of index of refraction and

thickness L = 320 nm, that is suspended in air. At what wavelength is the light

reflected by the film brightest to an observer.

16. A slit of width is illuminated by white light (which consists of the entire

wavelength in the visible range). For what value of will the first minimum for red

light of wavelength =650 nm appear at ?

17. A glass lens is coated on one side with a thin film of Magnesium Fluoride (MgF2) to

reduce reflection from the lens surface. The index of refraction of MgF2 is 1.38; that

of the glass is 1.50. What is the least coating thickeness that eliminates (via

interference) the reflections at the middle of the visible spectrum ( =550 nm)?

Assume that the light is approximately perpendicular to the lens surface.

18. Three light waves combine at a certain point where their electric field components are

Find the resultant field at that point by adding the three fields and represent

the resultant light field in the form of resultant amplitude and resultant phase

as

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